A plug-in hybrid electric vehicle (PHEV) includes two power sources for delivering power to propel the vehicle. Typically, the first power source is an engine that consumes fuel to deliver power, and the second power source is a battery that uses stored electric energy to deliver power. The battery may be rechargeable from an on-board generator driven by the engine and/or an external electric power source, such as the electric utility grid.
Many consumers expect a PHEV to use electric energy whenever possible to minimize use of fuel due to the relatively lower-cost of grid supplied electric energy. As such, a PHEV may have two basic operating modes: a charge depleting (CD) mode; and a charge sustaining (CS) mode. In the CD mode, electric energy from the battery is used to propel the vehicle and depletes the stored electric energy as reflected in the associated battery state-of-charge (SOC). A vehicle system controller or the like controls the vehicle to prioritize power delivered by the battery, with engine power used to supplement battery power when needed to meet driver requirements. Once the battery SOC decreases to a predefined charge level, the vehicle is driven in the CS mode and primarily powered by the engine.
The CD mode includes an electric vehicle (EV) mode (i.e., an all-electric mode), a blended mode, and an engine mode. In the EV mode, only electric energy and no fuel energy is used to propel the PHEV. As recognized by the present disclosure, a typical PHEV is designed for limited EV mode operation (e.g., 25 kW). If the driver demands more power (e.g., 30 kW) than the EV system of the vehicle can deliver (i.e., 25 kW), then control transitions to the blended mode and the engine is started to meet the driver-demanded power. However, the engine of a typical PHEV is calibrated to operate near its peak efficiency (e.g., 20 kW), which often produces more power than needed to supplement the battery power and meet the driver demand (i.e., 30 kW−25 kW=5 kW in this example). Consequently, the vehicle not only consumes fuel during this period, but the vehicle consumes more fuel (i.e., 20 kW/η, where η=combustion efficiency) than needed to meet the driver-demanded power (i.e., 5 kW/η) with the excess engine power used to recharge the battery.
The CD range of a PHEV is the distance the vehicle can travel in the CD mode before switching to the CS mode. The CD range at a given time depends on the current battery SOC. The driver typically does not care about fuel efficiency in terms of fuel consumption per unit of power produced when the driver intends to drive a distance less than the CD range of the vehicle. Rather, when the distance to be driven is less than the CD range of the vehicle, the driver is generally more concerned about fuel economy (i.e., miles/gallon). Any relatively small increase in fuel consumption can drastically reduce fuel economy such as from 500 mi/gal to 60 mi/gal thereby disappointing the driver.